feat(props): add connection mode closes #702

src/components/Handle/handler.ts

@@ -0,0 +1,171 @@
+import { MouseEvent as ReactMouseEvent } from 'react';
+
+import {
+  ElementId,
+  XYPosition,
+  OnConnectFunc,
+  OnConnectStartFunc,
+  OnConnectStopFunc,
+  OnConnectEndFunc,
+  ConnectionMode,
+  SetConnectionId,
+  Connection,
+} from '../../types';
+
+type ValidConnectionFunc = (connection: Connection) => boolean;
+export type SetSourceIdFunc = (params: SetConnectionId) => void;
+
+type Result = {
+  elementBelow: Element | null;
+  isValid: boolean;
+  connection: Connection;
+  isHoveringHandle: boolean;
+};
+
+// checks if element below mouse is a handle and returns connection in form of an object { source: 123, target: 312 }
+function checkElementBelowIsValid(
+  event: MouseEvent,
+  connectionMode: ConnectionMode,
+  isTarget: boolean,
+  nodeId: ElementId,
+  handleId: ElementId | null,
+  isValidConnection: ValidConnectionFunc
+) {
+  const elementBelow = document.elementFromPoint(event.clientX, event.clientY);
+  const elementBelowIsTarget = elementBelow?.classList.contains('target') || false;
+  const elementBelowIsSource = elementBelow?.classList.contains('source') || false;
+
+  const result: Result = {
+    elementBelow,
+    isValid: false,
+    connection: { source: null, target: null, sourceHandle: null, targetHandle: null },
+    isHoveringHandle: false,
+  };
+
+  if (elementBelow && (elementBelowIsTarget || elementBelowIsSource)) {
+    result.isHoveringHandle = true;
+
+    // in strict mode we don't allow target to target or source to source connections
+    const isValid =
+      connectionMode === ConnectionMode.Strict
+        ? (isTarget && elementBelowIsSource) || (!isTarget && elementBelowIsTarget)
+        : true;
+
+    if (isValid) {
+      const elementBelowNodeId = elementBelow.getAttribute('data-nodeid');
+      const elementBelowHandleId = elementBelow.getAttribute('data-handleid');
+      const connection: Connection = isTarget
+        ? {
+            source: elementBelowNodeId,
+            sourceHandle: elementBelowHandleId,
+            target: nodeId,
+            targetHandle: handleId,
+          }
+        : {
+            source: nodeId,
+            sourceHandle: handleId,
+            target: elementBelowNodeId,
+            targetHandle: elementBelowHandleId,
+          };
+
+      result.connection = connection;
+      result.isValid = isValidConnection(connection);
+    }
+  }
+
+  return result;
+}
+
+function resetRecentHandle(hoveredHandle: Element): void {
+  hoveredHandle?.classList.remove('react-flow__handle-valid');
+  hoveredHandle?.classList.remove('react-flow__handle-connecting');
+}
+
+export function onMouseDown(
+  event: ReactMouseEvent,
+  handleId: ElementId | null,
+  nodeId: ElementId,
+  setConnectionNodeId: SetSourceIdFunc,
+  setPosition: (pos: XYPosition) => void,
+  onConnect: OnConnectFunc,
+  isTarget: boolean,
+  isValidConnection: ValidConnectionFunc,
+  connectionMode: ConnectionMode,
+  onConnectStart?: OnConnectStartFunc,
+  onConnectStop?: OnConnectStopFunc,
+  onConnectEnd?: OnConnectEndFunc
+): void {
+  const reactFlowNode = (event.target as Element).closest('.react-flow');
+
+  if (!reactFlowNode) {
+    return;
+  }
+
+  const handleType = isTarget ? 'target' : 'source';
+  const containerBounds = reactFlowNode.getBoundingClientRect();
+  let recentHoveredHandle: Element;
+
+  setPosition({
+    x: event.clientX - containerBounds.left,
+    y: event.clientY - containerBounds.top,
+  });
+
+  setConnectionNodeId({ connectionNodeId: nodeId, connectionHandleId: handleId, connectionHandleType: handleType });
+  onConnectStart?.(event, { nodeId, handleId, handleType });
+
+  function onMouseMove(event: MouseEvent) {
+    setPosition({
+      x: event.clientX - containerBounds.left,
+      y: event.clientY - containerBounds.top,
+    });
+
+    const { connection, elementBelow, isValid, isHoveringHandle } = checkElementBelowIsValid(
+      event,
+      connectionMode,
+      isTarget,
+      nodeId,
+      handleId,
+      isValidConnection
+    );
+
+    if (!isHoveringHandle) {
+      return resetRecentHandle(recentHoveredHandle);
+    }
+
+    const isOwnHandle = connection.source === connection.target;
+
+    if (!isOwnHandle && elementBelow) {
+      recentHoveredHandle = elementBelow;
+      elementBelow.classList.add('react-flow__handle-connecting');
+      elementBelow.classList.toggle('react-flow__handle-valid', isValid);
+    }
+  }
+
+  function onMouseUp(event: MouseEvent) {
+    const { connection, isValid } = checkElementBelowIsValid(
+      event,
+      connectionMode,
+      isTarget,
+      nodeId,
+      handleId,
+      isValidConnection
+    );
+
+    onConnectStop?.(event);
+
+    if (isValid) {
+      onConnect?.(connection);
+    }
+
+    onConnectEnd?.(event);
+
+    resetRecentHandle(recentHoveredHandle);
+    setConnectionNodeId({ connectionNodeId: null, connectionHandleId: null, connectionHandleType: null });
+
+    document.removeEventListener('mousemove', onMouseMove);
+    document.removeEventListener('mouseup', onMouseUp);
+  }
+
+  document.addEventListener('mousemove', onMouseMove);
+  document.addEventListener('mouseup', onMouseUp);
+}